"Rivers change course over many lifetimes, and eventually all bridges tumble down. A thousand years ago there was another city on this spot. The people carved the bones of whales and inscribed them with my Mark. Children still find them washed up in the river-mud."
Okay, so usually right before Bill appears, the people entering his black-and-white dreamscape zone close their eyes, showing that they’ve fallen asleep and gone into a Bill-controlled dream.
So isn’t it odd that Dipper didn’t close his eyes when the black and white zone went off and Bill appeared, but instead just a few moments before? It was after he shut his eyes that the laptop told him there were too many failed attempts.
But that never happened.The laptop wouldn’t have erased anything, Because Bill Cipher was tricking up the dream before even the audience knew Dipper was asleep.
"Someone’s getting desperate!" You waited, Bill, you waited until Dipper was tired and frustrated beyond measure, waited until he was at the point where he wasn’t really concentrating or trying, and then you made your move.